With reference to FIG. 1, low-frequency radio frequency identification (RFID) system (125-134 kHz) and a high-frequency radio frequency identification (RFID) system (13.56 MHz) transmit signals within a distance of several cm to 1 M. A transmission range of UHF radio frequency identification (RFID) system (860-960 MHz) is up to 10 M. A transmission rage of microwave frequency band RFID system (2.4 GHz) is up to 30M. Thus, the UHF radio frequency identification (RFID) system and the microwave frequency band RFID system are applied to sense sensed targets in a long distance.
Referring to FIG. 2, methods and systems for integrated interrogation of RFID sensors are disclosed in U.S. Pat. No. 8,717,146. To sense targets accurately, multiple spectrum parameters (such as frequency positions (FP) of Zre(f) and magnitude Zp(f),) resonance (F1), and anti-resonance (F2) are measured. When airs attach on a RFID sensor, dielectric constants of sensing films change so as to alter impedance parameters of RFID sensor antenna.
Methods and systems for calibration of RFID sensors are disclosed in U.S. Pat. No. 7,911,345 and contains RFID antenna made of sensing material configured to change response of impedance as airs attaches on the sensing material. A complementary sensor resistance and/or a capacitor are connected with an antenna and IC memory chip so as to calibrate impedance response of the RFID sensors.
Systems and methods for monitoring sensors are disclosed in US Publication No. 20140095102, wherein sensing material layers is coated on high frequency (HF) and ultrahigh frequency (UHF) RFID antenna, and one specific of the sensing materials is coated on one of tags, but each tag is merely configured to sense one target. A long-distance RFID sensor is configured to sense explosive, yet the high-frequency RFID sensor cannot be used to sense targets in a long distance.
Identifiable ticket and monitoring system therefor are disclosed in U.S. Pat. No. 9,594,992 B1, wherein the identifiable ticket contains a body and a radio frequency identification (RFID) tag attached on the body. The RFID tag includes a chip and an antenna, the chip stores an identified message, and the antenna is electrically connected with the chip. The body includes a ticket stub and at least one separable part removable from the ticket stub so as to tear off the antenna, hence the RFID tag responds reading operations of at least one tag reader in different frequency bands and distances after the antenna is torn off or based on a length of the antenna. A monitoring system for the identifiable ticket contains the identifiable ticket, a computer, and the at least one tag reader. The at least one tag reader is connected with the computer and reads the RFID tag so as to acquire and to send the identified message to the computer. After the body is torn off, the RFID tag responds reading operation to readers of various tags in different bands and distances. However, the RFID tag cannot senses multiple targets of various physical or chemical properties.
Printed radio frequency sensor structure and a method of preparing a RFID sensor tag is disclosed in U.S. Pat. No. 9,639,800 B2, wherein the Printed radio frequency sensor contains: a substrate, a RF antenna arranged on a top surface of the substrate, and a protection layer covering on the RF antenna arranged, wherein plural sensing materials are directly introduced into a RF antenna mixture of the RF antenna. A method of preparing a RFID sensor tag comprising steps of: A). Printing conductive sensing ink/glue on substrate; B. Drying, curing and compressing the conductive sensing ink/glue to form a conductive antenna mixture with plural sensing materials; C). Bonding a chip on a RFID sensing antenna to form a RFID sensor tag; and D). Coating a protection layer on a top of the RFID sensor tag. Here note protection coating can fully, partially or no cover the conductive sensing antenna. However, the printed radio frequency sensor structure merely responds reading operation of a sole tag reader in a single band.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.